I actually ended up having my specialty of interest first (again, got my last choice track lol) but it worked out great for me.  My school has a light schedule and some vacation time between Step 1 and the first rotation, so I had time to do a little reading/preparing before starting the rotation.  I honored my clinical evals (not the shelf, but let's be real I am never going to honor any of the shelves anyway).  It also gave me a chance to connect early with mentors in the field, the residents and faculty at my home program, potential LOR writers, etc.  I could go back and shadow them whenever I had time, meet with them for advising, and get hooked up with research and networking opportunities, all because they already knew me and (I think/hope) liked me from working with me on the rotation.  Granted, the specialty I'm applying to is less competitive and has more warm-fuzzy type of people to begin with.  I wouldn't recommend it to everyone, but I don't think it's the end of the world if you get stuck with your preferred specialty first.